How To Avoid Burring w/ brass v-carve?

[joelschuman]

I'm v-carving free-machining brass plate, line engraving, 90deg carbide v-bit, .015" total depth of cut. The consensus on feeds/speeds, found by searching here and elsewhere, is 20,000-25,000 RPM, .5 ips, .010" first pass with .005" final pass. I'm getting a considerable amount of burring along the edges. That suggests metal is melting, and means I need to reduce spindle speed or increase feed rate. I'd like to avoid the trial and error approach, since this can't be an uncommon task. Who's done this before? Has anyone got the 411 on this? I'd like to avoid a secondary polishing operation if possible - I have acres of this stuff to cut! Thanks.

[Brady Watson]

Joel,
You don't need to spin the router that fast. Bring it down to around 13,000 and try your current move speed. You will also do well to rig up an air coolant line, which you can piece together for a few bucks using brass fittings and an air hose. You only need about 25psi blowing on the bit.

The bit itself should have a very small flat on the tip to give the chips some place to go. I recommend an engraving bit like the 1/4" shank ones sold by Micro100, or buy a solid carbide mill/drill which has a 90° tip.

Trial and error? You're not going to get around that. Keep a watchful eye (wear glasses!!!!) and ear on what is going on and make adjustments as you go. Keep the Z speed between .1 & .3 IPS to avoid stalling the Z if you are using a PRT. Once you get your setting right, WRITE THEM DOWN!

-B